Medical Diagnostic Testing in the Developing World

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Medical Diagnostic Testing in the Developing World[edit | edit source]

Conventional laboratory diagnostics are of limited availability in the developing world. Labs are constrained because of the cost of equipment for conventional tests and lack of well-trained staff. Often diagnoses are based on symptoms which can lead to overdiagnosis of common illnesses such as malaria. Misdiagnosed patients are at risk of side effects from the drugs they are given and from worsening condition due to the illness that they do have that was not diagnosed. Additionally, drug resistances can develop when people are given inappropriate antibiotics.

Many alternatives are being considered for methods of providing point-of-care clinical diagnostic testings. Various types of rapid diagnostic tests are in use currently. First, flow-through tests involved flushing a set of reagents, starting with the sample (blood, urine, etc) to be tested through a membrane held in a cassette-type frame. This type of test does not run on its own. It can be done one or a few at a time. It requires a liquid sample. Kits are available for flow-through diagnostic tests. Secondly, there are strip tests that work like pregnancy tests by giving the user a clear two lines for yes, one line for no and no lines for a null result response. Liquid and semisolid samples can both be used, and the tests, once set up can be set aside to finish. The tester does not need to provide any additional attention. Thirdly, in solid phase tests the sample is placed on a solid substrate, which is incubated. Then, it is washed be a series of reagents which contain identifiers (EIA, protein A, sensitized latex particles). Finally, agglutination tests, which give visual confirmation of the presence of a pathogen based on the creation of an agglutinate are also available. These tests are difficult in cases of weak presence of an antigen. They can be hard to interpret in such cases. All of these types of tests search for protein matter. This means that assay search the sample for either antigens directly or for antibodies the host has produced against an antibody. This type of assay has some disadvantages. For example, one cannot distinguish between a current and past infection. (2) There is also a wide range of sensitivity (1)

Other methods include microscopy which requires having a microscope and a skilled operator. Microscopy can be used for “parasitic and mycobacterial” infections (1). Bacteria are grown and cultured in labs for more rigorous tests. This can involve incubation of up to weeks for certain illnesses (3). Cultures however allow drug resistance testing (1). The downside to this type of testing is that there are strict storage requirements for the samples, there is a lot of infrastructure that needs to be in place for it to be viable (uninterrupted electricity, trained staff), and it is expensive. Nucleic acid amplification tests (NAAT) are highly specific and sensitize and are viable for multiple types of pathogen (bacteria and viruses). However, for conventional NAAT methods one needs specialized equipment and training. Avoiding contamination is a big concern with this type of test.

Our method takes only liquid samples. It only extracts DNA, after which some sort of test must still be performed on the product to give a diagnosis. We cannot store results for reference. Nucleic acid based tests allow for monitoring drug resistance of samples. While antigen/antibody tests can test for the presence of a disease, they cannot test for particular drug resistances whereas molecular tests can provide this information.

References

(1) http://www.who.int/std_diagnostics/publications/Diagnostics%20for%20the%20developing%20world.pdf (2) http://www.rapid-diagnostics.org (3) FIND website said that ideal time for TB was 6 weeks.